Question

A beaker is filled with water to a height of 8.00 cm. The apparent depth of a needle fixed at the bottom of the beaker as measured by a travelling microscope is found to be 6.00 cm. If the height of water in the beaker is increased to 12.0 cm, by what distance would the microscope have to be moved to focus on the needle again?       

Solution

Correct option is

3 cm

 

Real depth is 8.00 cm and apparent depth is 6.00 cm. Therefore, refractive index of water is

                         

When the real depth of water is increased to 12.0 cm, the apparent depth would become  

                               

Therefore, the distance through which the microscope has to be moved to focus on the needle is 9.00 – 6.00 = 3.00 cm.

SIMILAR QUESTIONS

Q1

A plano-concave lens is made of glass of refractive index 1.5 and the radius of curvature of the curved face is 50 cm. The power of the lens is

Q2

A convex lens of focal length 50 cm and a concave lens of focal length 100 cm are separated by a distance of 10 cm. What is the power of the combination?    

Q3

How will the image formed by a convex lens be affected if the central portion of the lens is wrapped in black paper, as shown in fig.

                                                                            

Q4

The equi-convex lens, shown in the figure, has a focal length f. What will be the focal length of each half if the lens it cut along AB? (See fig.)

                                                                   

Q5

A person can see clearly only up to a distance of 30 cm. He wants to read a book placed at a distance of 50 cm from his eyes. What is the power of the lens he requires for his spectacles?   

Q6

A person with defective eyesight is unable to see objects clearly nearer than 1.5 m. He wants to read a book placed at a distance of 30 cm from his eyes. Find the power of the lens he requires for his spectacles.   

Q7

An object, a convex lens of focal length 20 cm and a plane mirror are arranged as shown in fig. How far behind the mirror is the final image formed? 

                                                         

Q8

A small plane mirror is rotating at a constant frequency of n rotations per second. With what linear velocity (in ms–1) will a light spot move along a spherical screen of radius of curvature of R metres if the mirror is at the centre of curvature of the screen?   

Q9

A ray of light incident normally on face AB of an isosceles prism travels as shown in fig. The least value of the refractive index the prism must have should be    

                                                                        

Q10

When a thin wedge-shaped film is illuminated by a parallel beam of light of wavelength 6000 Ã…, 7 fringes are observed in a certain region of the film. How many fringes will be observed in the same region of the film if light of wavelength 4200 Ã… is used?